Application of sequence hopping and orthogonal covering codes to uplink reference signals

ABSTRACT

Methods and User Equipment (UE) apparatuses are provided for transmitting Reference Signals (RSs). A method includes receiving a cell-specific sequence-hopping parameter; receiving a UE-specific sequence-hopping parameter; determining a reference signal sequence based on the UE-specific sequence-hopping parameter; and transmitting the reference signal based on the determined reference signal sequence. Sequence hopping does not apply to the reference signal sequence if the cell-specific sequence-hopping parameter indicates that the sequence hopping is enabled and the UE-specific sequence-hopping parameter indicates that the sequence hopping is disabled.

PRIORITY

The present application is a Continuation of U.S. application Ser. No. 13/032,257, which was filed in the United States Patent and Trademark Office on Feb. 22, 2011, and claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application No. 61/306,753, entitled “Applying Orthogonal Covering Codes to Uplink Reference Signals,” which was filed in the United States Patent and Trademark Office on Feb. 22, 2010, the entire disclosure of each of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to wireless communication systems and, more particularly, to enhancing the functionality and enabling features of reference signals transmitted from a User Equipment. The reference signals provide an estimate of the channel medium experienced by the User Equipment at a given time instance.

2. Description of the Related Art

Several types of signals need to be supported for the proper functionality of a communication system. In addition to data signals, conveying the information content, control signals also need to be transmitted from User Equipments (UEs) to their serving Base Station (BS or NodeB) in the UpLink (UL) of the communication system and from the serving NodeB to the UEs in the DownLink (DL) of the communication system to enable proper processing of the data signals. For example, control signals include positive or negative ACKnowledgement signals (ACK or NACK, respectively) that are transmitted in response to (correct or incorrect, respectively) data packet reception and are associated with a Hybrid Automatic Repeat reQuest process (HARQ-ACK signals). Control signals also include Channel Quality Indication (CQI) signals, which a UE sends to the NodeB to provide information about the DL channel conditions that the UE experiences. Further, Reference Signals (RS), also known as pilot signals, are typically transmitted to provide channel estimation and enable coherent demodulation for the transmitted data or control signals or, in the UL, to be used by the receiving NodeB to measure the UL channel conditions the UE experiences. The former RS used for demodulation of data or control signals will be referred to as DeModulation RS (DMRS) while the latter RS, which are typically wideband in nature, are used for sounding the UL channel medium and will be referred to as Sounding RS (SRS).

A UE, also commonly referred to as a terminal or a Mobile Station, may be fixed or mobile and may be a wireless device, a cellular phone, a personal computer device, and the like. A NodeB is generally a fixed station and may also be referred to as a Base Transceiver System (BTS), an access point, or similar terminology.

UEs transmit data or control information through a Physical Uplink Shared CHannel (PUSCH) while, in the absence of PUSCH transmission, the UEs transmit control information through a Physical Uplink Control CHannel (PUCCH). A UE receives the signals conveying data information through a Physical Downlink Shared CHannel (PDSCH) while signals conveying control information are received through a Physical Downlink Control CHannel (PDCCH).

A UE is assumed to transmit in the PUSCH or in the PUCCH over a Transmission Time Interval (TTI), which may, for example, correspond to a sub-frame with a duration of 1 millisecond (msec). FIG. 1 illustrates a block diagram of a sub-frame structure 110 for PUSCH transmission. The sub-frame includes two slots. Each slot 120 includes seven symbols. Each symbol 130 further includes a Cyclic Prefix (CP) in order to mitigate interference due to channel propagation effects. Some symbols in each slot may be used for the DMRS transmission 140. The second DMRS in the sub-frame may or may not be transmitted with its negative value (scaled with “−1”) 150 as it is subsequently described. The PUSCH transmission BandWidth (BW) consists of frequency resource units, which will be referred to as Resource Blocks (RBs). In one example, each RB includes N_(sc) ^(RB)=12 sub-carriers, which are also referred to as Resource Elements (REs). A UE may be allocated one or more RBs 160 for PUSCH transmission and one RB for PUCCH transmission.

PUSCH transmission or PDSCH reception by a UE may be scheduled by the NodeB either dynamically, through a respective Scheduling Assignment (SA) conveying a Downlink Control Information (DCI) format in a PDCCH, or through Semi-Persistent Scheduling (SPS) using UE-specific higher layer signaling such as Radio Resource Control (RRC) signaling. The DCI format may inform a UE about a data packet transmission by the NodeB in the PDSCH (DL SA) or about a data packet transmission to the NodeB (UL SA) in the PUSCH. With SPS, a UE transmits or receives data packets at predetermined sub-frames.

FIG. 2 illustrates a processing chain at the NodeB for a SA transmission. The Media Access Control (MAC) layer IDentity of the UE (UE ID) for which the SA is intended for masks the Cyclic Redundancy Check (CRC) of the SA information bits in order to enable the UE to identify that the SA is intended for it. The CRC 220 of the SA information bits 210 is computed and then masked 230 using the eXclusive OR (XOR) operation between CRC bits and UE ID bits 240. An XOR operation only evaluates to true where only one of the two input bits is 1. Thus, XOR(0,0)=0, XOR(0,1)=1, XOR(1,0)=1, XOR(1,1)=0. The masked CRC is then appended to the SA information bits 250, channel coding (such as convolutional coding) is performed 260, followed by rate matching 270 to the allocated PDCCH resources, and finally by interleaving and modulation 280, and transmission of the SA 290. It is assumed that both the CRC and the UE ID have the same length such as, for example, 16 bits.

The UE receiver performs the reverse operations of the NodeB transmitter. This is illustrated in FIG. 3. The received control signal 310 is demodulated and the resulting bits are de-interleaved 320, the rate matching applied at the NodeB transmitter is restored 330 and then followed by decoding 340. The SA bits 360 are then obtained after extracting the CRC bits 350, which are then de-masked 370 by applying the XOR operation with the UE ID 380. Finally, the UE performs the CRC check 390. If the CRC check passes, the UE considers the SA as a valid one and determines the parameters for signal reception (DL SA) or signal transmission (UL SA). If the CRC check does not pass, the UE disregards the presumed SA.

The DMRS is assumed to be generated from Constant Amplitude Zero Auto-Correlation (CAZAC) sequences. An example of such a sequence is given by the following Equation (1):

$\begin{matrix} {{c_{k}(n)} = {\exp\left\lbrack {\frac{j\; 2\;\pi\; k}{L}\left( {n + {n\frac{n + 1}{2}}} \right)} \right\rbrack}} & {{Eq}.\mspace{14mu}(1)} \end{matrix}$ where L is a length of the CAZAC sequence, n is an index of a sequence element, n=[0, 1, 2, . . . , L−1], and k is a sequence index. For CAZAC sequences of length L, with L being a prime number, the number of sequences is L−1. Therefore, an entire family of sequences is defined as k ranges in [1, 2, . . . , L−1]. However, the sequences for DMRS transmission need not be generated by strictly using the above expression. As one RB is assumed to include N_(sc) ^(RB)=12 REs, CAZAC-based sequences can be generated either by truncating a longer prime length (such as length 13) CAZAC sequence or by extending a shorter prime length (such as length 11) CAZAC sequence by repeating its first element(s) at the end (i.e., cyclic extension), although the resulting sequences do not strictly fulfill the definition of a CAZAC sequence. Alternatively, CAZAC sequences can be generated through a computer search for sequences satisfying the CAZAC properties.

FIG. 4 shows an DMRS transmitter structure at a UE based on a CAZAC sequence. The frequency domain version of a CAZAC sequence may be obtained by applying a Discrete Fourier Transform (DFT) to its time domain version. The frequency domain CAZAC-based sequence 410 is generated, the REs 420 in the assigned PUSCH transmission BW are selected 430, the Inverse Fast Fourier Transform (IFFT) is performed 440, the Cyclic Shift (CS) 450 is applied, and, finally, the CP 460 and filtering 470 are applied to the transmitted signal 480. The UE also applies zero padding in REs where the DMRS is not transmitted, such as in REs used for signal transmission from another UE (not shown). The PUSCH transmission BW may be contiguous, in accordance with the SC-FDMA transmission principle, or non-contiguous in accordance with the DFT-Spread-OFDM (DFT-S-OFDM) transmission principle. For brevity, additional transmitter circuitry such as digital-to-analog converter, analog filters, amplifiers, and transmitter antennas, as they are known in the art, are not shown.

The NodeB receiver performs the reverse functions of the UE transmitter. This is illustrated in FIG. 5 where the reverse operations of those in FIG. 4 are performed. In FIG. 5, an antenna receives the Radio-Frequency (RF) analog signal and after passing further processing units (such as filters, amplifiers, frequency down-converters, and analog-to-digital converters) the resulting digital received signal 510 passes through a time windowing unit 520 and the CP is removed 530. Subsequently, the CS of the transmitted CAZAC-based sequence is restored 540, a Fast Fourier Transform (FFT) 550 is applied, the selection 560 of the transmitted REs 565 is performed, and correlation 570 with the CAZAC-based sequence replica 580 is applied. The resulting output 590 can then be passed to a channel estimation unit, such as a time-frequency interpolator.

In addition to the DMRS transmission, the transmission from a UE of control signals or RS in the PUCCH and their reception by the NodeB may also be based on CAZAC sequences and be respectively performed as previously described.

Different CSs of a CAZAC sequence provide orthogonal sequences. Therefore, for a given CAZAC sequence, different CSs can be allocated to different UEs and achieve orthogonal DMRS multiplexing in the same RBs. This principle is illustrated in FIG. 6. In order for the multiple CAZAC sequences 610, 630, 650, and 670 generated from multiple corresponding CSs 620, 640, 660, and 680 of the same CAZAC sequence to be orthogonal, the CS value 690 should exceed the channel propagation delay spread D (including a time uncertainty error and filter spillover effects). If T_(S) is the duration of one sub-frame symbol, the number of CSs is equal to └T_(s)/D┘ where └ ┘ denotes the “floor” operation which rounds a number down to its lower integer.

For a PUSCH transmission associated with an UL SA, the UL SA is assumed to include a Cyclic Shift Indicator (CSI) indicating the CS for the CAZAC sequence used as DMRS. For SPS PUSCH transmissions, the NodeB also provides, through higher layer signaling, to the UE the CSI value. Table 1 shows a mapping of CSI values to CS values.

TABLE 1 Mapping of CSI Values to CS Values. CSI Value CS Value 000 CS₀ = 0 001 CS₁ = 6 010 CS₂ = 3 011 CS₃ = 4 100 CS₄ = 2 101 CS₅ = 8 110  CS₆ = 10 111 CS₇ = 9

CAZAC-based sequences of the same length typically have low cross-correlations, which is important for minimizing mutual interference. CAZAC-based sequences of different lengths have a wide distribution of cross-correlation values and large values often occur. FIG. 7 shows the Cumulative Density Function (CDF) of cross-correlation values for length-12 CAZAC-based sequences resulting from cyclically extending a length-11 Zadoff-Chu (ZC) sequence, truncating a length-13 ZC sequence, or computer generation of length-12 CAZAC sequences. Variations in cross-correlation values are observed and even larger cross-correlation values may occur between CAZAC-based sequences of different lengths. Randomization of the occurrence of large cross-correlations can be achieved by sequence hopping where the sequence is selected from a predetermined set of sequences according to a hopping pattern such, as for example, a pseudo-random pattern having the slot number as one of its arguments.

Sequence hopping is among CAZAC-based sequences of the same length that belong either to the same group or to different groups. A group of CAZAC-based sequences consists of sequences with different lengths, each corresponding to each of the possible PUSCH RB allocations. For example, if 30 CAZAC-based sequences exist for the minimum allocation of 1 RB and since the number of available CAZAC-based sequences increases as the number of RBs increases, 30 sequence groups can always be generated. For large RB allocations, such as at least 6 RBs, 2 sequences can be included in each group of CAZAC-based sequences. Sequence hopping among sequences in different groups will be referred to as group sequence hopping while sequence hopping among sequences in the same group (for allocations of at least 6 RBs) will just be referred to as sequence hopping. Group sequence hopping and sequence hopping (within the same sequence group) are respectively enabled or disabled by the NodeB for all UEs in its cell and for all applicable signals using transmission of sequences (DMRS in the PUSCH or control signals and RS in the PUCCH) through broadcast signaling of the respective (cell-specific) parameters: Group-hopping-enabled and Sequence-hopping-enabled.

Multi-User Multiple-Input Multiple-Output (MU-MIMO) can improve the spectral efficiency of a communication system. With MU-MIMO, PUSCH transmissions from multiple UEs share at least part of a BW. MU-MIMO is facilitated if the NodeB can obtain interference-free estimates of the channel medium the MU-MIMO UEs experience. This requires orthogonal reception for the respective DMRS. If the PUSCH transmissions from MU-MIMO UEs share exactly the same BW, orthogonal DMRS multiplexing can be obtained using different CS of the same CAZAC sequence. However, if the PUSCH transmissions from MU-MIMO UEs do not share exactly the same BW, orthogonal DMRS multiplexing using different CS is not possible because the respective CAZAC-based sequences have different lengths. Orthogonal Covering Codes (OCC) can then be used to provide orthogonal DMRS multiplexing in the time domain. For the sub-frame structure in FIG. 1 which has 2 DMRS symbols, the OCCs can be {1, 1} and {1, −1}. Regarding the CS, the OCC should also be indicated for the DMRS transmission in the PUSCH.

Two classes of UEs are assumed to coexist in the communication system. The first class of UEs, referred to as legacy-UEs, do not support OCC and rely only on the CS for orthogonal DMRS multiplexing. The second class of UEs, referred to as Advanced-UEs, support OCC and can rely on both OCC and CS for orthogonal DMRS multiplexing.

A required restriction for the application of OCC is the absence of sequence hopping Because of the sub-frame structure in FIG. 1, time-domain orthogonality is not possible if the DMRS transmission in each sub-frame slot uses a different CAZAC sequence. Therefore, although OCC is only needed by Advanced-UEs for MU-MIMO transmissions over different BWs, the performance of all UEs is degraded by the requirement to disable sequence hopping over the entire cell. Moreover, as sequence planning to achieve low cross-correlations is typically impractical, PUCCH transmissions, which are assumed to rely entirely on CAZAC sequences, and occur over only one RB are particularly impacted which is highly undesirable given that control information has enhanced reliability requirements.

Therefore, there is a need to define a mapping of CSI values to OCC and CS values that optimizes DMRS multiplexing among Advanced-UEs and among legacy-UEs and Advanced-UEs.

There is also need to enable sequence hopping in a cell while supporting time-domain orthogonality through the application of OCC for the DMRS transmission in the PUSCH.

Finally, there is need to separate the application of sequence hopping between sequences used in PUSCH transmissions and sequences used in PUCCH transmissions.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been designed to solve at least the aforementioned problems in the prior art and the present invention provides methods and an apparatus to support the configuration of the DMRS transmission parameters, through the application of a CS and an OCC, to disable sequence hopping for the DMRS in PUSCH transmissions from a UE when sequence hopping is enabled in the cell, and to separate the application of sequence hopping between PUSCH and the PUCCH.

In accordance with an aspect of the present invention, a method is provided for a UE to transmit a reference signal. The method includes receiving a cell-specific sequence-hopping parameter; receiving a UE-specific sequence-hopping parameter; determining a reference signal sequence based on the UE-specific sequence-hopping parameter; and transmitting the reference signal based on the determined reference signal sequence. Sequence hopping does not apply to the reference signal sequence if the cell-specific sequence-hopping parameter indicates that the sequence hopping is enabled and the UE-specific sequence-hopping parameter indicates that the sequence hopping is disabled.

In accordance with another aspect of the present invention, a UE is provided for transmitting a reference signal. The UE includes a transceiver configured to receive a cell-specific sequence-hopping parameter, to receive a UE-specific sequence-hopping parameter, and to transmit the reference signal, based on a reference signal sequence; and a controller configured to determine the reference signal sequence based on the UE-specific sequence-hopping parameter. Sequence hopping does not apply to the reference signal sequence if the cell-specific sequence-hopping parameter indicates that the sequence hopping is enabled and the UE-specific sequence-hopping parameter indicates that the sequence hopping is disabled.

In accordance with another aspect of the present invention, a method is provided for a UE to transmit a reference signal. The method includes receiving a cell-specific sequence-hopping parameter; receiving a UE-specific sequence-hopping parameter; identifying a type of the reference signal; determining a reference signal sequence based on the UE-specific sequence-hopping parameter, when the reference signal is of a first type; and transmitting the reference signal based on the determined reference signal sequence. Sequence hopping does not apply to the reference signal sequence for the reference signal of the first type, if the cell-specific sequence-hopping parameter indicates that the sequence hopping is enabled and the UE-specific sequence-hopping parameter indicates that the sequence hopping is disabled.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagram illustrating a UL sub-frame structure for PUSCH transmission in the UL of the communication system;

FIG. 2 is a block diagram illustrating the coding process of a SA in the NodeB;

FIG. 3 is a block diagram illustrating the decoding process of a SA in the UE;

FIG. 4 is a block diagram illustrating a transmitter structure for a CAZAC-based sequence;

FIG. 5 is a block diagram illustrating a receiver structure for a CAZAC-based sequence;

FIG. 6 is a diagram illustrating the orthogonal RS multiplexing using different cyclic shifts of a CAZAC sequence;

FIG. 7 is a diagram illustrating the Cumulative Density Function (CDF) of cross-correlation values for length-12 CAZAC-based sequences;

FIG. 8 is a diagram illustrating the interpretation of the mapping of CSI values to CS and OCC values depending on the use of group sequence hopping or sequence hopping within a group;

FIG. 9 is a diagram illustrating the application of sequence hopping depending on the “OCC-enabled” parameter value the NodeB informs the UE through RRC signaling; and

FIG. 10 is a diagram illustrating the different applicability of sequence hopping in the PUSCH and in the PUCCH depending on the “OCC-enabled” parameter and the cell-specific enabling of sequence hopping.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The present invention will now be described more fully hereinafter with reference to the accompanying drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope of the invention to those skilled in the art.

Additionally, although the present invention is described in relation to a Single-Carrier Frequency Division Multiple Access (SC-FDMA) communication system, it also applies to all Frequency Division Multiplexing (FDM) systems in general and to an Orthogonal Frequency Division Multiple Access (OFDMA), OFDM, FDMA, Discrete Fourier Transform (DFT)-spread OFDM, DFT-spread OFDMA, SC-OFDMA, and SC-OFDM system in particular.

The following two goals are considered:

a) Defining a mapping of CSI values to CS and OCC values, which optimizes DMRS multiplexing among Advanced-UEs and among legacy-UEs and Advanced-UEs.

b) Enabling sequence hopping in the PUSCH in conjunction with the application of OCC.

The first goal considers that the CSI value provides signaling support for orthogonal DMRS multiplexing among UEs also in the time domain by indicating a respective OCC value in addition to a CS value. The conventional CSI Information Element (IE) remains unchanged and no additional bits are introduced in the CSI IE to indicate that the OCC is being applied to the DMRS. Instead, the CSI value provides mapping to both the CS and the OCC values.

The CSI IE is assumed to consist of 3 bits and address a CS from a set of eight CS, {CS₀, CS₁, CS₂, CS₃, CS₄, CS₅, CS₆, and CS₇}. For example, for a CAZAC-based sequence r(n) in the frequency domain, where n is the RE index, the DMRS sequence is r^((α))(n)=e^(jαn) r(n) where α is the CS given as α=2πn_(CS)/12 where n_(CS)=(N_(DMRS)+n_(DMRS))mod 12 and N_(DMRS) is a cell-specific values that is common to all UEs in a cell and n_(DMRS) is determined from the CSI.

For legacy-UEs, the mapping in Table 1, and the goal of selecting CS values with the largest mutual distance in the time domain (modulo 12), the optimal CS values for various numbers of MU-MIMO legacy-UEs are:

a) 2 MU-MIMO legacy-UEs: CS₀ and CS₁

b) 3 MU-MIMO legacy-UEs: CS₀, CS₃ and CS₅

c) 4 MU-MIMO legacy-UEs: CS₀, CS₁, CS₂ and CS₇.

For more the 4 MU-MIMO legacy-UEs, the optimal CS values practically consist of the first 4 ones, CS₀, CS₁, CS₂ and CS₇, and any other additional values. Legacy-UEs are assumed to not support OCC for their DMRS transmission and therefore they have the implicit assignment of OCC {1, 1}. Since the communication system is assumed to support both legacy-UEs and Advanced-UEs, the OCC {1, 1} will be implicitly used by legacy-UEs and will not be as readily available to Advanced-UEs as the OCC {1, −1}. Rules for the CSI to OCC/CS mapping for Advanced-UEs will now be considered.

The first rule is that the CSI values indicating OCC {1, 1} should indicate different CS values for Advanced-UEs than for legacy-UEs in order to maximize MU-MIMO capacity among legacy-UEs and Advanced-UEs.

The second rule is that an equal number of CSs is associated with OCC {1, 1} and with OCC {1, −1}. For a CSI consisting of 3 bits indicating a total of 8 CS/OCC combinations, this implies that 4 CS values are associated with OCC {1, 1} and 4 CS values are associated with OCC {1, −1}.

The third rule is that different CSs associate with OCC {1, 1} and with OCC {1, −1}. Then, DMRS orthogonal multiplexing is achieved both through OCC and through CS, which enhances its robustness against temporal channel variations or large channel propagation delays.

The fourth rule is that CS values associated with OCC {1, 1} have maximum mutual distance and CS values associated with OCC {1, −1} also have maximum mutual distance.

The above rules also allow the NodeB to arbitrarily select any CSI value while ensuring a robust mapping of the CSI values to CS and OCC values. This is important because the CSI may also be used to indicate the resource for the corresponding HARQ-ACK signal transmission from the NodeB (in response to the reception by the NodeB of the PUSCH transmission by the UE in case it is scheduled by the UL SA containing the CSI).

Table 2 shows the mapping of the CSI values to the CS and OCC values used for the DMRS transmission by Advanced-UEs in accordance with the previously described rules.

TABLE 2 First Mapping of CSI Values to CS and OCC Values—Advanced-UEs. CSI Value CS Value OCC Value 000 2   {1, −1} 001 8   {1, −1} 010 5   {1, −1} 011 1 {1, 1} 100 7 {1, 1} 101 4 {1, 1} 110 10 {1, 1} 111 11   {1, −1}

The mapping in Table 3 also satisfies the CSI to CS-and-OCC mapping rules. Relative to the mapping in Table 2, the only difference is that the association between CS values and OCC values is reversed.

TABLE 3 Second Mapping of CSI Value to CS and OCC Values—Advanced-UEs. CSI Value CS Value OCC Value 000 1   {1, −1} 001 7   {1, −1} 010 4   {1, −1} 011 2 {1, 1} 100 8 {1, 1} 101 5 {1, 1} 110 11 {1, 1} 111 10   {1, −1}

In principle, the association of a specific CSI value with a pair of CS and OCC values can be arbitrary and not confined to ones in Table 2 or Table 3. For example, an alternative association may be used such as Table 4 or Table 5 below. This is because the previously described rules consider only the association between CS and OCC values for Advanced-UEs and their relation to the CS values for legacy-UEs. In this respect, the CSI value associated with a CS/OCC pair is immaterial. Nevertheless, the association of a CSI value with a pair of CS and OCC values in Table 2 or Table 3 is beneficial.

TABLE 4 Third Mapping of CSI Value to CS and OCC Values—Advanced-UEs. OCC CSI Value CS Value Value 000 2   {1, −1 } 001 8   {1, −1} 010 5   {1, −1} 011 11   {1, −1} 100 1 {1, 1} 101 7 {1, 1} 110 4 {1, 1} 111 10 {1, 1}

TABLE 5 Fourth Mapping of CSI Value to CS and OCC Values—Advanced-UEs. CSI Value CS Value OCC Value 000 5   {1, −1} 001 11   {1, −1} 010 8   {1, −1} 011 1 {1, 1} 100 7 {1, 1} 101 4 {1, 1} 110 10 {1, 1} 111 2   {1, −1}

The second goal considers enabling DMRS sequence hopping in conjunction with the application of OCC in the PUSCH. DMRS sequence hopping needs to be disabled in case of MU-MIMO among UEs having PUSCH transmission with different bandwidths in order to allow for orthogonal DMRS multiplexing relying on different OCCs.

Since the Node B can control whether sequence hopping (either across groups of sequences or within a group of sequences) is applied to its cell and can control whether MU-MIMO transmissions are over different PUSCH bandwidths, it can select between these two features (sequence hopping or MU-MIMO over different PUSCH bandwidths). If the (cell-specific) “group-hopping-enabled” and the “sequence-hopping-enabled” parameters indicate that sequence hopping is disabled in the cell served by the NodeB, the mapping of CSI values to OCC/CS values can be, for example, as in Table 2, Table 3, Table 4, or Table 5. If the “group-hopping-enabled” or the “sequence-hopping-enabled” parameter indicates that sequence hopping is enabled in the cell, the CSI mapping to CS values for Advanced-UEs can be as in Table 1.

FIG. 8 illustrates the interpretation by an Advanced-UE of the mapping from the CSI values to CS and OCC values. If the NodeB indicates 810 that either group sequence hopping or sequence hopping within a group is enabled 820, an Advanced-UE assumes that the CSI indicates only CS values 830, for example using the mapping in Table 1. Otherwise 840, an Advanced-UE assumes that the CSI indicates both CS and OCC values 850, for example using the mapping in Table 2.

Alternatively, a new (UE-specific) parameter “OCC-enabled” can be defined for Advanced-UEs in order to separate the application of sequence hopping among legacy-UEs and Advanced-UEs. The “OCC-enabled” parameter is signaled through RRC to the Advanced-UE and indicates whether sequence hopping is enabled or not (and may also interpret the CSI as mapping to both CS and OCC values or as mapping only to CS values) when the NodeB already indicates (through cell-specific signaling) that sequence hopping is enabled in its cell. In the first case, the Advanced-UE follows the indication of the “group-hopping-enabled” and “sequence-hopping-enabled” parameters by the NodeB regarding sequence hopping. In the second case, the Advanced-UE disables both group sequence hopping and sequence hopping within a group even when the (cell-specific) “group-hopping-enabled” and “sequence-hopping-enabled” parameters indicate that sequence hopping is enabled.

FIG. 9 illustrates the mapping of CSI values to CS and OCC values and the application of sequence hopping by an Advanced-UE depending on the value of the “OCC-enabled” parameter signaled by the NodeB. An Advanced-UE evaluates whether “OCC-enabled=Enabled” 910 and if the NodeB indicates that it is enabled 920 (implying sequence hopping is disabled), the Advanced-UE may assume that the CSI value indicates both a CS value and an OCC value 930, using, for example, the mapping in Table 2, and the Advanced-UE does not apply sequence hopping to its DMRS transmission regardless of the respective (cell-specific) NodeB indication for sequence hopping. Otherwise, if OCC-Enabled is not enabled 940, the Advanced-UE may assume that the CSI value indicates only CS values, using, for example, the mapping in Table 1, and follows the (cell-specific) NodeB indication regarding sequence hopping for its DMRS transmission 950.

Since signal transmissions in the PUCCH are assumed to occur in one RB, only group sequence hopping can apply for the respective CAZAC-based sequences (which, in addition to DMRS, may include HARQ-ACK signals or CQI signals). As the restrictions regarding sequence hopping from the introduction of OCC do not occur in the PUCCH, an Advanced-UE is assumed to always follow the (cell-specific) indication of the “group-hopping-enabled” parameter by the NodeB regardless of the (UE-specific) indication for sequence hopping and application of OCC for the DMRS transmission in the PUSCH (through the UE-specific “OCC-enabled” parameter).

FIG. 10 illustrates the different applicability of the cell-specific “group-hopping-enabled” parameter for CAZAC-based sequence hopping in the PUSCH and in the PUCCH depending on the “OCC-enabled” parameter. If the “group-hopping-enabled” parameter 1010 indicates that group hopping for CAZAC-based sequence is not enabled 1020, group sequence hopping of CAZAC-based sequences does not apply either in the PUSCH or in the PUCCH 1030. If the “group-hopping-enabled” parameter indicates that group hopping for CAZAC-based sequence is enabled 1040, then group hopping of CAZAC-based sequences in the PUSCH depends on the “OCC-enabled” parameter 1050. If the “OCC-enabled” parameter is not set 1060, group sequence hopping of CAZAC-based sequences applies to both PUSCH and PUCCH 1070. If the “OCC-enabled” parameter is set 1080, group sequence hopping of CAZAC-based sequences applies only to PUCCH 1090.

While the present invention has been shown and described with reference to certain embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the appended claims and their equivalents. 

What is claimed is:
 1. A method of a User Equipment (UE) for transmitting a reference signal, the method comprising: receiving a cell-specific sequence-hopping parameter; receiving a UE-specific sequence-hopping parameter; determining a reference signal sequence based on the UE-specific sequence-hopping parameter; and transmitting the reference signal based on the determined reference signal sequence, wherein sequence hopping is not applied to the reference signal sequence when the cell-specific sequence-hopping parameter indicates that the sequence hopping is enabled and the UE-specific sequence-hopping parameter indicates that the sequence hopping is disabled.
 2. The method of claim 1, wherein the cell-specific sequence-hopping parameter and the UE-specific sequence-hopping parameter are transmitted by higher-layer signaling.
 3. The method of claim 1, wherein the cell-specific sequence-hopping parameter is transmitted by broadcast signaling to a plurality UEs including the UE, and wherein the UE-specific sequence-hopping parameter is transmitted by UE-specific signaling to the UE.
 4. The method of claim 1, wherein the reference signal includes a reference signal for a Physical Uplink Shared CHannel (PUSCH).
 5. The method of claim 1, wherein the sequence hopping includes sequence-group hopping.
 6. The method of claim 1, wherein the UE-specific sequence-hopping parameter includes an “Orthogonal Complementary Code (OCC)-enabled” parameter.
 7. The method of claim 1, further comprising generating the reference signal using Constant Amplitude Zero Auto-Correlation (CAZAC) sequences.
 8. A User Equipment (UE) for transmitting a reference signal, the UE comprising: a transceiver configured to receive a cell-specific sequence-hopping parameter, to receive a UE-specific sequence-hopping parameter, and to transmit the reference signal, based on a reference signal sequence; and a controller configured to determine the reference signal sequence based on the UE-specific sequence-hopping parameter, wherein sequence hopping is not applied to the reference signal sequence when the cell-specific sequence-hopping parameter indicates that the sequence hopping is enabled and the UE-specific sequence-hopping parameter indicates that the sequence hopping is disabled.
 9. The UE of claim 8, wherein the cell-specific sequence-hopping parameter and the UE-specific sequence-hopping parameter are transmitted by higher-layer signaling.
 10. The UE of claim 8, wherein the sequence-hopping parameter is transmitted by broadcast signaling to a plurality UEs including the UE, and wherein the UE-specific sequence-hopping parameter is transmitted by UE-specific signaling to the UE.
 11. The UE of claim 8, wherein the reference signal includes a reference signal for a Physical Uplink Shared CHannel (PUSCH).
 12. The UE of claim 8, wherein the sequence hopping includes sequence-group hopping.
 13. The UE of claim 8, wherein the controller is configured to determine whether a sequence hopping for a reference signal of a Physical Uplink Control CHannel (PUCCH) is enabled based on the cell-specific sequence-hopping parameter.
 14. The UE of claim 8, wherein the UE-specific sequence-hopping parameter includes an “Orthogonal Complementary Code (OCC)-enabled” parameter.
 15. The UE of claim 8, wherein the controller is configured to generate the reference signal from Constant Amplitude Zero Auto-Correlation (CAZAC) sequences.
 16. A method of a User Equipment (UE) for transmitting a reference signal, the method comprising: receiving a cell-specific sequence-hopping parameter; receiving a UE-specific sequence-hopping parameter; identifying a type of the reference signal; determining a reference signal sequence based on the UE-specific sequence-hopping parameter, when the reference signal is of a first type; and transmitting the reference signal based on the determined reference signal sequence, wherein sequence hopping is not applied to the reference signal sequence for the reference signal of the first type, when the cell-specific sequence-hopping parameter indicates that the sequence hopping is enabled and the UE-specific sequence-hopping parameter indicates that the sequence hopping is disabled.
 17. The method of claim 16, further comprising determining the reference signal sequence based on the cell-specific sequence-hopping parameter, when the reference signal is of a second type.
 18. The method of claim 17, wherein the reference signal of the second type is a reference signal of a Physical Uplink Control CHannel (PUCCH).
 19. The method of claim 16, wherein the reference signal of the first type is a reference signal of a Physical Uplink Shared CHannel (PUSCH).
 20. The method of claim 16, wherein the cell-specific sequence-hopping parameter and the UE-specific sequence-hopping parameter are transmitted by higher-layer signaling. 